1. Field of the Invention
The present invention relates to an electric motor. More particularly, the present invention relates to an electric motor in which polarities of a stator and the number of polarities thereof are converted by converting the polarity of current depending on a rotation position of a rotor made of a permanent magnet so as to enhance the attraction and repulsion occurring between the rotor and the stator, so that a rotative force of the rotor can be achieved with minimum power.
2. Discussion of the Related Art
A motor is a rotary machine which converts electrical energy to mechanical energy. Generally, a direct current (DC) motor driven by a DC power source includes a stator of a permanent magnet, fixably mounted on an outer side of a main body, a rotor rotated by attraction and repulsion with the stator, and a brush for supplying current to a coil in contact with the rotor. The rotor includes an iron core fixably mounted on a rotary shaft to be rotated, a coil wound in the iron core to provide the iron core with an electromagnetic property by means of current applied to the iron core, and a commutator for supplying current to the coil.
A conventional DC motor will be described with reference to FIGS. 1a and 1b.
FIG. 1a is a longitudinal sectional view illustrating a conventional DC motor.
Referring to FIG. 1a, a stator 10 includes a first permanent magnet 2 and a second permanent magnet 3. The first permanent magnet 2 and the second permanent magnet 3 are mounted in an inner wall of a main body 1 to oppose each other at a predetermined distance.
A rotor 20 includes a plurality of commutators 23, iron cores 25, and coils 24. The plurality of commutators 23 separated from each other by a predetermined distance are fixably mounted at one side of a shaft 21 by means of combining members 22. The iron cores 25 are fixably mounted at a predetermined distance from the commutators 23. First to eighth folders 25a.about.25h are radially formed in an inner side of the iron cores 25. In the first to eighth folders 25a.about.25h, the coils 24 are wound in one direction through the commutators 23.
A first brush 5 and a second brush 6 are elastically mounted at one side of an inner wall of a cover 4 in contact with the commutators 23. The first and second brushes 5 and 6 supply power to the coil 24 to provide the iron cores 25 with an electromagnetic property.
In the aforementioned conventional DC motor, as illustrated in FIG. 1a, the positive "+" power source is applied to the first brush 5 and the negative "-" power source is applied to the second brush 6. The first and second brushes 5 and 6 are in contact with the commutators 23 to flow current into the coil 24 so that the first to eighth folders 25a.about.25h of the iron cores 25 become electromagnets each having a particular polarity, respectively.
Therefore, the first to eighth folders 25a.about.25h of the iron cores 25 and the first and second permanent magnets 2 and 3 mutually generate attraction and repulsion to rotate the rotor 20 which includes the iron cores 25, the coil 24 and the commutators 23.
As illustrated in FIG. 1b, it is assumed that the positive "+" power source is applied to the wound coil 24 of the first folder 25a through the first brush 5 and the commutators 23 and the negative "-" power source is applied to the wound coil 24 of the fifth folder 25e through the second brush 6 and the commutators 23. In that case, the second to fourth folders 25b.about.25d become electromagnets having N polarity and the sixth to eighth folders 25f.about.25h become electromagnets having S polarity.
Therefore, repulsion occurs between the first permanent magnet 2 and the third and fourth folders 25c and 25d because of the same N polarity and repulsion occurs between the second permanent magnet 3 and the seventh and eighth folders 25g and 25h because of the same S polarity. At the same time, attraction occurs between the second permanent magnet 3 and the sixth and seventh folders 25f and 25g because of different polarities, and attraction occurs between the first permanent magnet 2 and the second and third folders 25b and 25c because of different polarities. As a result, the rotor 20 rotates clockwise.
The aforementioned conventional DC motor has several problems.
First, the rotor of the conventional DC motor includes the iron cores having the plurality of folders, fixably mounted on the shaft, the coil wound in the folders, and the commutators for supplying the current to the coil. This structure complicates the configuration of the rotor and causes increased load when rotating the rotor, thereby reducing the rotative force of the rotor.
Further, in the conventional DC motor, since half of the folders formed in the iron cores have an N polarity and the other folders have an S polarity, attraction and repulsion occur partially in a longitudinal end portion of the permanent magnet of the stator and in some of the folders of the rotor disposed at the longitudinal end portion. Therefore, a certain rotative force is maintained. However, to generate a high rotative force, it is necessary to supply more current to the coil through the commutators. As a result, power consumption increases.
In this respect, development of an electric motor having a high rotative force at a low power is required.